In order to make a claim to R&D tax credit, the SME will need to submit a Corporation Tax return, CT600, and tax computation. The CT600 will need to include form CT600L, and the information requested on the CT600L forms part of the mandatory requirements.
The online form available through the webpage linked in your email is not mandatory, and is available to help customers to support their claims.
We have included below a link to the Corpoate Intangibles Research and Development manual, page CIRD 81800, which has more information about making a claim, including a link to guidance on the HMRC website on how to complete the form CT600L:
CIRD81800 - R&D tax relief: conditions to be satisfied: claims and time limits