One person builds Delta. Email support@deltastrength.app and that person reads it. There is no ticket system, no bot, and no tier of support you can pay to reach.
Tell me what happened and what you expected instead. Two things make a bug findable, and without them I am usually guessing:
Screenshots help more than descriptions. Your workout data never leaves your device, so I cannot look at it from here, which means what you tell me is genuinely all I have.
Delta exists because I wanted a workout notebook that did not want an account, a subscription, or my data. It is shaped by using it: almost everything in the app arrived because it was annoying in a gym, not because it looked good on a roadmap.
If something is in your way, say so. I will not promise to build every request, and I would rather tell you no than let you wait on something that is never coming. But an owner explaining what does not work is the most useful thing I get, and a lot of what is in Delta today started exactly that way.
You pay once.
The reason this is possible is that Delta is small on purpose. It costs almost nothing to run, because there is nothing to run: no servers, no accounts, no analytics pipeline. A subscription would be charging you rent on software that does not have any.
So you can decide whether it is for you before you pay:
Delta is made by Lesko Technology Solutions LLC.