Royal Mail are making changes to the STL and BPL service codes which will come into place from April 2020; Shiptheory is aware of these changes but at the current moment no changes need to be made on either the Shiptheory side or your side.
These changes only will be necessary for sales orders, meaning that your Shiptheory orders will not be affected. As stated by Royal Mail:
"From the 1st of April 2020, the Royal Mail STL and BPL product codes should cease to be used via OBA Sales Orders. STL/BPL will continue to be available for use via shipping solutions."
Any changes that are required in the future, either on the Shipthory side or your side, we'll make sure to let you know.