[ECS] [Issue]: describe-services API call is showing error while using service name in format "ClusterName/ServiceName" in ap-south-2 region

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>> describe-services API call is showing error while using service name in format "ClusterName/ServiceName" in ap-south-2 region only while in other regions it is working fine.

> In ap-south-2 region, it is showing below error:

$ aws ecs describe-services --cluster Cluster --services "Cluster/ser2" --region ap-south-2

An error occurred (InvalidParameterException) when calling the DescribeServices operation: Service contains invalid separators

However, If I use only service name, it is working fine:

aws ecs describe-services --cluster Cluster --region ap-south-2 --services "ser2"
{
"services": [
{
"serviceArn": "arn:aws:ecs:ap-south-2:5619xxxx6291:service/Cluster/ser2",
"serviceName": "ser2",
"clusterArn": "arn:aws:ecs:ap-south-2:5619xxxx6291:cluster/Cluster",
"loadBalancers": [],
"serviceRegistries": [],
"status": "ACTIVE",
"desiredCount": 1,
"runningCount": 1,
....
....

> While, In eu-central-1 or other regions, it is working fine irrespective of Service name format :

$ aws ecs describe-services --cluster Cluster --region eu-central-1 --services "Cluster/ser2"
{
"services": [
{
"serviceArn": "arn:aws:ecs:eu-central-1:9814xxxxx36:service/Cluster/ser2",
"serviceName": "ser2",
"clusterArn": "arn:aws:ecs:eu-central-1:9814xxxxx36:cluster/Cluster",
"loadBalancers": [],
"serviceRegistries": [],
"status": "ACTIVE",

OR

$ aws ecs describe-services --cluster Cluster --region eu-central-1 --services "ser2"
{
"services": [
{
"serviceArn": "arn:aws:ecs:eu-central-1:9814xxxx536:service/Cluster/ser2",
"serviceName": "ser2",
"clusterArn": "arn:aws:ecs:eu-central-1:9814xxxxx36:cluster/Cluster",
"loadBalancers": [],

Note:
1. AWS CLI version is latest (aws-cli/2.14.4 Python/3.11.6 Darwin/22.6.0 exe/x86_64 prompt/off).
2. IAM role is having proper IAM permission to invoke ECS API calls.

=====

**Which service(s) is this request for?**
This could be Fargate, ECS.

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
What outcome are you trying to achieve, ultimately, and why is it hard/impossible to do right now? What is the impact of not having this problem solved? The more details you can provide, the better we'll be able to understand and solve the problem.

**Are you currently working around this issue?**
How are you currently solving this problem?

The current workaround - describe-services API call works if only service name mentioned.

**Additional context**
Anything else we should know?

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

Start by reproducing the two aws ecs describe-services commands shown for ap-south-2 and eu-central-1, comparing the ClusterName/ServiceName and service-name-only forms. No repository file or test is identified; done means determining whether the regional behavior is an AWS ECS service issue and documenting a confirmed resolution or next step.

Written by the indexing model from the issue text.