Hi @hbroker
Please have a look at the Blockonomics checkouts: Blockchain API | Bitcoin API - Blockonomics
This api endpoint allows you to add custom data to your payment button, such as user_id, before displaying the button to the user. eg.
curl -H 'Authorization: Bearer 2cDNOlCN985d7Rx3atSDOlmMeYaxzho2uPmHheIw4eU' -d'{"parent_uid": "f7570454529a11e7", "extra_data":"user_id-19120"}' https://www.blockonomics.co/api/create_temp_product
This api endpoint will return a temp product uid like this f7570454529a11e7-1ee5f340, which you can set to a payment button. eg.
<a href="" class="blockoPayBtn" data-toggle="modal" data-uid=f7570454529a11e7-1ee5f340><img width=160 src="https://www.blockonomics.co/img/pay_with_bitcoin_medium.png"></a>
Please let me know if you have any further questions regarding setting up the payment buttons with extra data.
Kind regards