Firstly you will need to navigate to Credit Control > Settings and select the Reminders template.

You can then remove the invoice link from reminders by removing the highlighted line of text that includes the 'Invoice Link for Customers' Snippet field, by using the backspace or delete key on your keyboard:

What is a Snippet?

Remember to save each template you amend

You may also want to remove the View Invoice link from the Grouped reminders template. Here you will need to remove the Snippet called 'Grouped Open Invoices Table' using the backspace or delete key on your keyboard.

Then click on the # button to add an invoices table snippet without invoice links:

Select the snippet 'Grouped Open Invoice Table without Links to Invoices':
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You may also want to remove a similar Snippet from the Statement template if you have this template also enabled. It is a similar task which also involves removing the current invoices table that you can replace with 'Open Invoices Table without Links to Invoices':