Why can't I press Next?

List what may be stopping Next on the current step: empty required fields, firing Set Errors and validations, and custom components.

Next is greyed out, or it does nothing, and the screen does not say why. The Structure tab keeps a list of what may be stopping it on the step the script is on. It is judged against the data right now and it is a best effort, so read it as a short list of suspects.

Find the step and its count

Open the Structure tab and pick your OmniScript. Follow current step is on by default, so the step the script is on stays selected. If you have browsed away, press Current step.
Look at the step's row. A small red number means that many things may stop Next on it. There is no number at zero. The step's head says the same as "May stop Next: N". See May stop Next count.
Look down the Valid column: a ✕ on a field would stop Next, and the step's ✕ is their sum. See Valid column.
Open the step's Validation tab. It appears while something may stop Next on the step, or while the step holds a custom component. See Step validation.

Read the cards

The Validation tab is a column of cards, judged against the data right now, best effort:

Required and empty. The visible required elements of the step whose value is empty. A required checkbox must be ticked. Fields inside an Edit Block are left out: they are checked when the row is saved.
Validation rules. One card per Set Errors or Messaging / Validation rule: failing ones open, passing ones folded to one line. Each shows Field · Must be · Is now with a ✓ or ✗ per condition and a plain-words reading under it. Info and Warning messages stop no one.
Custom components. One folded card each, with the verdict of its show rule.

Click a name to select that element and see why it counts. A hidden required field is not listed, because only visible required elements count. See Why is this field hidden?.

Repeat rows

For an element inside a Repeat Block or Edit Block, the detail head shows "Row 1 of 3" with ‹ › buttons. Step through the rows. The step's Validation tab follows the row you chose, and rows count from 1, as in OmniScript paths. See Repeat rows.

Set Errors and validations

Open the element's Validation tab to see whether its condition is true now and which message it shows. Its Is now cells can be edited, as on the Visibility tab, to see which value would make the error go away. Nothing is written to the page. See Validation tab and What if.

If errors start to fire while you are on another tab, a toast says so, for example "Set Errors fire on Intro: 2". See Set Errors toast.

What the list cannot see

A custom component may carry its own required controls or its own Next and Previous buttons. These cannot be read from the definition, which is why the tab only reminds you of them.
Server-side checks, and rules the panel cannot evaluate, are not covered.
A finding that rests only on a formula's estimate is listed apart under Estimated and is not counted. See Formulas.

If the list is empty and Next still fails, the reason is probably in a call. Open Calls and read Why did this call fail, and what did it send?.

Copy report, in the Tools row of Settings (the gear), includes what may stop Next on the current step. See Report a problem.