Error 90004 — Required attribute missing for variation child

A variation child is missing the attribute(s) it needs to differentiate from its siblings — e.g., a 'Size' theme parent has a child without a size value.

If the parent's variation_theme is 'Size', every child MUST have a size attribute populated. Missing this attribute on any child triggers 90004 for that child.

1. Identify the variation theme on the parent (e.g., Size, Color, SizeColor).
2. Fill in the corresponding attribute(s) on EVERY child — no blanks allowed.
3. Use consistent format across children (e.g., all size values as 'S/M/L' or all as 'Small/Medium/Large', not mixed).
4. Resubmit the affected children only — parent doesn't need re-submission.

• Submitting size as 'M' for some children and 'Medium' for others — Amazon treats them as different sizes
• Leaving the size blank for a one-size-fits-all SKU within a multi-size variation family — use 'OS' or 'One Size'