https://HTLC.me is an awesome testnet Lightning wallet for playing with test invoices.
Discussion
testnet lightning is such fucking shit
but yeah, htlc.me is about the best you can get
true story:
when I wrote the LN implementation for swan I was so annoyed by testnet LN routing failures (and couldn't really use Polar easily when trying more real things in dpeloyed infra)
I just put some sats of my own on a node and and started using real LN for my tests 😂
Ha. That was my strategy..
But then I found out that BTCPay has a testnet lightning demo instance. And then HTLC.me payments worked fine. Which is enough for me to learn and test things end to end for now.