To create Payment Links:

Step 1 - Integrate Sub-Account With Stripe: 

Integrate the sub-account with Stripe by going to Settings > Payments and click the "Connect Your Stripe Account" button and follow the steps to integrate Stripe.

Step 2 - Create An Invoice From A Conversation:

Go to a conversation and click the payment icon below the text editor. In the modal that pops up, give the Invoice a name, price, and then set a Link Expiration/Due Date and hit Save. The payment link will then appear in the conversation editor.