Is your scientific paper or presentation the result of STSM, of discussions or collaborations developed thanks to a meeting or other SyMat events? Is your presentation given at a conference you attend funded by an ITC grant? If so, an acknowledgement of the SyMat Action is then necessary.
Rules for COST acknowledgements are here: https://www.cost.eu/uploads/2022/01/COST_actions-guidelines2022.pdf
Acknowledgement in papers
“This publication is based upon work from COST Action Symat (CA18223), supported by COST (European Cooperation in Science and Technology)”.