If mobile users cannot complete the form comfortably, start by preserving one representative example. It gives the investigation a concrete reference and makes the eventual correction easier to judge.
Find the likely cause
Field controls and layout were checked only on desktop.
Treat this as an explanation to verify against the actual work. Look at the input, the relevant decision, and the final result together. If the evidence does not support this diagnosis, investigate the mismatch before applying a convenient but unrelated fix.
Make the targeted correction
Use appropriate input behavior and test on a small screen.
A form should request the information needed for the next step while making expectations and recovery clear.
Check that the repair worked
Complete the full form with a mobile keyboard and visible error messages.
Repeat the check on the final version that the reader or customer will encounter. An approved draft, a preview, and a published result can differ; the acceptance decision should concern the version people actually use.
Prevent the next related failure
A separate issue to watch for is this: the form asks for information customers cannot yet provide. Separate essential initial fields from later discovery questions.
Monitor the useful outcome
Track successful submissions, field errors, inquiry quality, and device-specific completion issues.
Keep a short record of the original symptom, the evidence behind the diagnosis, and the result of the acceptance check. That record makes the solution reusable when the same condition appears again, without assuming that every superficially similar problem has the same cause.