What to do when an API has no documentation - rest

Question

I'm currently trying to use a REST API to insert data from Powershell into a Jira custom field made by a certain plugin (Easy links for JIRA). Unfortunately there's no documentation on the required syntax. Does anyone who's run into this plugin know the commands/syntax I'll need to use the REST API (It's quite a small plugin so I'll be surprised if anyone else has seen it)? Failing that, does anyone have any advice on discovering how to use APIs with no/bad documentation i.e. some standard method of making an API return a list of commands and syntax (preferably by using powershell)?
I've tried contacting the developer but haven't heard back from them.
The code I'm using is here, if that's helpful:
function Test-Upload(){
Param()
Process{
$data=#"
{
"fields":
{
"project":
{
"key": "CCWASSET"
},
"summary": "Testing Linked Field",
"issuetype":
{
"name": "Asset"
},
"description" : "Testing Linked Field"
},
"update":{
"customfield_10500":[
{
"set":{
"type":{
"name":"Asset PO",
"inward":"Asset",
"outward":"Purchase Order"
},
"outwardIssue":{
"key":""
}
}
}
]
}
}
"#
return Jira-WebRequest -data $data
}
}
function Jira-WebRequest(){
Param(
[Parameter(mandatory=$false)]$data,
[Parameter(mandatory=$false)]$requesttype="issue",
[Parameter(mandatory=$false)]$method="POST",
[Parameter(mandatory=$false)]$ContentType='application/json'
)
Process{
$path = $("/rest/api/2/$requesttype/")
$Uri = ""
[URI]::TryCreate([URI]::new($Settings.Jira.URL),"$path",$([ref]$Uri))
$Params = #{
ContentType = $ContentType
Body = $data #$(#{"vlan_id"=$vlanID;"port_id"="$portID";"port_mode"="$portMode"} | ConvertTo-JSON)
Method = $method
URI = $uri.AbsoluteUri
Headers = $JiraHeaders
#WebSession = $Session
}
try{
$result = Invoke-RestMethod #Params -Verbose
return $result
} Catch [System.Net.WebException] {
$exception = $_.Exception
$respstream = $exception.Response.GetResponseStream()
$sr = new-object System.IO.StreamReader $respstream
$ErrorResult = $sr.ReadToEnd()
return $ErrorResult
}
}
}

Answer 1

It doesn't matter if the custom field made by a plugin or by you. At the end it's custom field so since the plugin doesn't have a good documentation, I would recommend you to stay with Atlassian Documentation and update / edit your issues base on official REST API. You can see Atlassian examples with Custom Fields here
What you need to do is you just need to figure out what's the custom field ID and that would be easy by going towards admin panel and clicking on the custom field and check it from URL if you don't want to go to database.
I know it's pain to see API without documents but at least you can workaround it this way.

Answer 2

Managed to get it working for this particular plugin. Had to include the ID field as well as the Key of the issue that I want to link to. I'd still be interested to hear if anyone has some tips for working with API's that have no/bad documentation.
"update":{
"customfield_10500":[
{
"set":{
"type":{
"name":"Asset PO",
"inward":"Asset",
"outward":"Purchase Order"
},
"outwardIssue":{
"key":""
"ID":""
}
}
}
]
}
}