put (one's) money where (one's) mouth is

Translations
подкрепить слова делом
If someone believes in the project, they should put their money where their mouth is.
Если кто-то верит в проект, он должен подкрепить слова делом.
Definitions
To back up one's words or claims with action or financial commitment, demonstrating that one truly believes in what they are saying.