How to implement a payment button?

You have two possibilities:

1- You can generate an invoice directly from your Paymium account by going to the drop-down menu in your Paymium space and clicking on 'Payment Solution'.
Depending on some criteria you have selected (desired conversion Euro vs Bitcoin, information requested from the customer such as email and/or postal address), a line of code will be generated.
You will have to add it in the code of your website page.
Then, you will have a Bitcoin payment button.

2- You can integrate our API and automate the invoice creation process by consulting the API documentation.