This error occurs when the parcel weight exceeds Royal Mail's maximum supported weight of 20 kg for the selected service.
Error message
"The shipment weight exceeds the max weight allowed (20kg) for this format and service."
What this means
The parcel is too heavy for the Royal Mail service selected. Royal Mail has a maximum weight limit of 20 kg per parcel.
How to fix it
Review the shipment weight.
Choose one of the following options:
Reduce the shipment weight if possible.
Split the return into multiple parcels, each under 20 kg.
Switch to a carrier that supports heavier shipments.
Regenerate the label.
If the issue continues
Contact support with the RMA ID and a screenshot of the error.