SMS payment reminders for overdue invoices from lexoffice and sevDesk

Connect lexoffice (Lexware Office) or sevDesk to TopSMS once, and your customers get a short SMS when an invoice is overdue: with the invoice number, the open amount and the due date. You decide on which days after the due date reminders go out, at what time of day and with which text.

MusterGmbHnow

Muster GmbH: your invoice RE-2026-0042 for 1.234,50 EUR is 10 days overdue (due on 15.09.2026). Please transfer the amount.

Second reminder, 10 days after the due date, with the amount still open.

3, 10, 21default reminder days after the due date, up to 5 stages
1 API keyno plugin, no export; TopSMS only reads
€0.084per SMS to Germany, Austria and the rest of the EU

How it works in 3 steps

Connect your invoicing tool. In lexoffice, create an API key under Add-ons, Public API; in sevDesk, copy the API token of an administrator. Paste it in the TopSMS dashboard under Invoice reminders. We check it right away with a live request and store it encrypted.
Set the rules. Choose the days after the due date (for example 3, 10 and 21), the text, the sender name, the hours in which SMS may go out, weekdays only, and a minimum amount below which nobody is reminded. The preview lists every overdue invoice with the SMS it would get, or the reason why not.
Reminders run by themselves. Every hour TopSMS loads the overdue invoices and sends the reminders that are due within your time window. Each reminder appears in the history with its status; paid invoices drop out on their own.

Which invoices get a reminder

lexoffice: invoices with the status open or overdue whose due date has passed. Drafts, paid and archived invoices are left out. The amount in the SMS is the open amount, so part payments are taken into account.
sevDesk: open and partly paid invoices whose payment term (invoice date plus payment term in days) has passed. Drafts, paid invoices, cancellations and recurring invoice templates are left out. The amount is the gross total minus what has already been paid.

Every reminder stage is sent at most once per invoice, and an invoice gets at most one SMS within 3 days, even if several stages are reached at once.

Where the phone number comes from

TopSMS reads the number from the customer record: in lexoffice from the contact’s phone numbers, in sevDesk from the contact’s phone entries. A mobile number is used first. A number without a country code, such as 0151 1234567, gets the code of the country in the customer’s billing address in lexoffice, otherwise +49.

German landline numbers are skipped, because a landline cannot receive the SMS. Customers without a usable number appear in the preview with the reason, so you can add the mobile number in your invoicing tool.

Short, polite and in one SMS

The default German text fits into one SMS with common values. Umlauts and ß belong to the GSM alphabet, so they do not shorten the message. The dashboard shows a sample with the character count and the number of SMS while you edit; a text longer than 3 SMS is not sent.

A message sent under your company name cannot be answered. If customers should call or write back, put a phone number or an email address in the text.

Reminder text and variables

The default English text and the variables you can use. The German default text is the same with German wording; Czech invoicing tools (Fakturoid, iDoklad) use the same feature with Czech variables.

{my}: your invoice {number} for {amount} is {days} days overdue (due on {due_date}). Please transfer the amount.

{number}        invoice number
{amount}        amount still open, with currency (1.234,50 EUR)
{amount_total}  invoice total
{due_date}      due date (15.09.2026)
{days}          days overdue
{customer}      customer name
{my}            your company name from the account settings

Reminders are ordinary SMS from your prepaid credit: no monthly fee for the feature, you pay only for the messages that are sent. You can also send reminders from your own code through the REST API.

Full API documentation →

Frequently asked questions

Which invoices does TopSMS remind?

In lexoffice, invoices with the status open or overdue whose due date has passed; in sevDesk, open and partly paid invoices whose payment term has passed. Drafts and paid invoices are never reminded, and the SMS shows the amount still open.

How often is a customer reminded?

Once per reminder stage you set, for example on day 3, 10 and 21 after the due date, with at most one SMS per invoice within 3 days. Up to 5 stages are possible, and SMS go out only in the hours you choose, optionally on weekdays only.

Can I see what will be sent before it goes out?

Yes. The preview loads the overdue invoices and shows for each one the SMS it would get, or why it is skipped (paid, below the minimum amount, no mobile number). Automatic reminders can be switched off at any time with one click.

Does TopSMS change anything in lexoffice or sevDesk?

No. TopSMS only reads invoices and contact phone numbers. The API key is stored encrypted, is not shown again and is deleted when you disconnect the account in the dashboard.

What does a payment reminder cost?

€0.084 per SMS to Germany, Austria and the rest of the EU, from prepaid credit and without a monthly fee. A reminder of up to 160 GSM characters, umlauts included, is one SMS.

Try it with 10 free SMS

Free account, active as soon as you confirm your mobile number. No credit card, no monthly fee, prepaid credit that never expires.

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