this snippet helps you to enable DIGITALOCEAN SPACES backup in vestacp.

vestacp-spaces-backup.sh

spaces_backup() {

    # Defining google settings
    #source $VESTA/conf/space.backup.conf
    export END_POINT=<ENTER THE ENDPOINT>
    export AWS_ACCESS_KEY_ID=<ENTER THE AWS ACCESS KEY>
    export AWS_SECRET_ACCESS_KEY=<ENTER THE AWS SECRET KEY>
    BUCKET=<YOUR BUCKET NAME HERE>
    BPATH=<DESTINATION PATH>

    gsutil="aws s3 --endpoint=${END_POINT}"
    export BOTO_CONFIG="$VESTA/conf/.space.backup.boto"

    # Debug info
    echo -e "$(date "+%F %T") Remote: s3://$BUCKET/$BPATH/$user.$backup_new_date.tar"

    # Checking retention
    # echo "aws s3 --endpoint=${END_POINT} ls s3://$BUCKET/$BPATH/$user.* 2>/dev/null"
    backup_list=$(aws s3 --endpoint=${END_POINT} ls s3://$BUCKET/$BPATH/$user.* 2>/dev/null)
    backups_count=$(echo "$backup_list" |wc -l)
    if [ "$backups_count" -ge "$BACKUPS" ]; then
        backups_rm_number=$((backups_count - BACKUPS))
        for backup in $(echo "$backup_list" |head -n $backups_rm_number); do 
            echo -e "$(date "+%F %T") Rotated spaces backup: $backup"
            aws s3 --endpoint=${END_POINT} rm $backup > /dev/null 2>&1
        done
    fi

    # Uploading backup archive
    echo -e "$(date "+%F %T") Uploading $user.$backup_new_date.tar ..."
    if [ "$localbackup" = 'yes' ]; then
        cd $BACKUP
        aws s3 --endpoint=${END_POINT} cp $user.$backup_new_date.tar s3://$BUCKET/$BPATH/ > /dev/null 2>&1
    else
        cd $tmpdir
        tar -cf $BACKUP/$user.$backup_new_date.tar .
        cd $BACKUP/
        # echo "aws s3 --endpoint=${END_POINT} cp $user.$backup_new_date.tar s3://$BUCKET/$BPATH/"
        aws s3 --endpoint=${END_POINT} cp /backup/$user.$backup_new_date.tar s3://$BUCKET/$BPATH/ > /dev/null 2>&1
        rc=$?
        rm -rf $user.$backup_new_date.tar
        rm -rf $tmpdir
        if [ "$rc" -ne 0 ]; then
            check_result "$E_CONNECT" "spaces failed to upload $user.$backup_new_date.tar"
        fi
    fi
}

add this snippet after google_backup() block and make sure add the line in switch case( Refer the image.)

And make sure you changed backup option to spaces in config/vesta.conf location