Error: You cannot change to this package because you are using integrated labels but this package does not support this feature. Please choose another package or delete your integrated labels.
In the event you have received this error but are not using Integrated labels, it can also be because of the use of Picking Lists.
You will need to delete the Picking List Templates from your account to successfully downgrade subscription which can be done here.
If you have any further questions, please do not hesitate to contact Shiptheory support!
Email: support@shiptheory.com
Telephone: (UK) +44 (0)117 403 4313 / (US) +1 (629) 6666726