most likely the flutter was not built by xcode cloud, try ci_post_clone.sh script https://docs.flutter.dev/deployment/cd#custom-build-script

Same: [!] Error installing PromisesObjC [!] /usr/bin/git clone https://github.com/google/promises.git /Volumes/workspace/tmp/d20231016-10650-c4fygs --template= --single-branch --depth 1 --branch 2.3.1

Just turned on the introductory price and a free trial for 1 week. Got 3 trials and all of them (different locations / countries) failed after 1 week period with billing error. RevenueCat ist obviously only consuming and forwarding this error. There must be something wrong at the core of billing mechanism or configuration in AppStore connect.