Why regex not work in bash in following situation? [duplicate]

BranchName=$1

RegEx="(refs\/heads\/)?([Rr]elease|[Dd]ev|hotfix)(-v[\d]+\.[\d]+\.[\d]+)(--)([\w][\w-]+)(--)[\d]+$"

echo "Branch name for test is: ${BranchName}"
if [[ ${BranchName} =~ ${RegEx} ]]; then
   echo "Branch name IN correct format: ${BranchName}"
   exit 0
else
   echo "Branch name not in correct format: ${BranchName}"
   exit 1
fi

string for testing: "refs/heads/release-v8.1.7--testBranchRename--323323"

REGEX correct according https://rubular.com/