I was able to integrate Payumoney India web checkout. Copied the HTML form and used dynamic inputs in the form, for redirect I used backend workflow, created backend workflow for all 3 redirect url parameters (surl,furl,curl) and created success and failure pages.
Setup detect data url in surl, furl and curl of the HTML form. And redirect to respective pages in the backend workflow.
For the first time setup, open the detect data window and run a transaction so that payu can send response data to bubble, once bubble detects the data you will see something like this:
Make changes to the transaction searching the transaction ID you received in the response data and save all the parameters of the transaction.
Once bubble detects the data remove the initialize in the surl,curl,furl in HTML form.