Modify invoice template

I’m trying to see how to get into the HTML code of the invoice templates on the Cloud edition but cannot find it?
Please Advise?

Ultimately what I want to do is add in code for a paymentlink that goes with the invoice to the customer so they can pay via their card to a payment gateway.

Read these Guides:

Thanks for that - the process seems a little different than when I used the Desktop version before moving to the Cloud.

With regards me including code for a payment link in the PDF invoice - is that something that is compatible with Manager?

Procedures for themes have changed. But they’ve changed for all editions, not just desktop.