How to Create/Modify iApp via API?

I am not sure exactly what is going wrong with your POST attempt as I cannot see the json data being posted. Below I copied a working script which will use the http template and allows you from a bash shell to input some of the common args you would expect. I have the JSON all in the same file for simplicity in troubleshooting, you could always pull it out into a separate file like you did.

Modifying answer as I submitted a new post with the code in a code block.

The post removed my comment symbols out, below should be correct as it is in a code block.

!/bin/bash
 This script will create an application service using the f5.http template.  Commandline arg... -a is iapp name, -v is virtual server ip, -m is for pool member ip,
 -b is the big ip address, -u is for username, -p for password (defaults of admin/admin if flags not present)  -d is an optional paramater if you would like to delete the iapp.
 Full Command would look like: ./createiapp_http.sh -b 2.2.2.2 -a httpapp -v 1.1.1.1 -m 1.1.1.2 -u admin -p admin
 Full Command to delete would add the delete flag: ./createiapp_http.sh -b 2.2.2.2 -a httpapp -v 1.1.1.1 -m 1.1.1.2 -u admin -p admin -d

delete=false
user=admin
pwd=admin
while getopts a:v:b:u:p:m:d option
do  case "$option"  in
        a) appname=$OPTARG;;
        v) vsip=$OPTARG;;
        m) pmember=$OPTARG;;
        b) bigip=$OPTARG;;
        u) user=$OPTARG;;
        p) pwd=$OPTARG;;
        d) delete=true;;
    esac 
done

echo "Delete equals: $delete"
echo "Connecting to BIG IP: $bigip as $user"
echo "iAPP Name: $appname"
echo "VS IP: $vsip"
echo "Pool Member: $pmember"

if [ $delete == false ] ;   then
curl -sk -u $user:$pwd https://$bigip/mgmt/tm/sys/application/service/ -H 'Content-Type: application/json' -X POST  -d '{"kind":"tm:sys:application:service:servicestate",

"name":'\"$appname\"',

"partition":"Common",

"execute-action":"definition",

"template":"/Common/f5.http",

"templateReference":{"link":"https://localhost/mgmt/tm/sys/application/template/~Common~f5.http?ver=12.0.0"},

"templateModified":"no",

"trafficGroup":"/Common/traffic-group-1",

"trafficGroupReference":{"link":"https://localhost/mgmt/tm/cm/traffic-group/~Common~traffic-group-1?ver=12.0.0"},

"tables":[{"name":"basic__snatpool_members"},

{"name":"net__snatpool_members"},

{"name":"optimizations__hosts"},

{"name":"pool__hosts",

"columnNames":["name"],"rows":[{"row":["test.test.com"]}]},

{"name":"pool__members",

"columnNames":["addr","port","connection_limit"],

"rows":[{"row":['\"$pmember\"',"80","0"]}]},

{"name":"server_pools__servers"}],

"variables":[{"name":"client__http_compression",

"encrypted":"no",

"value":"/create_new"},

{"name":"monitor__monitor",

"encrypted":"no","value":"/create_new"},

{"name":"monitor__response","encrypted":"no","value":"none"},

{"name":"monitor__uri","encrypted":"no","value":"/"},

{"name":"net__client_mode","encrypted":"no","value":"wan"},

{"name":"net__server_mode","encrypted":"no","value":"lan"},

{"name":"pool__addr","encrypted":"no","value":'\"$vsip\"'},

{"name":"pool__pool_to_use","encrypted":"no","value":"/create_new"},

{"name":"pool__port","encrypted":"no","value":"80"},

{"name":"asm__use_asm","value":"/do_not_use"},

{"name":"ssl__mode","encrypted":"no","value":"no_ssl"},

{"name":"ssl_encryption_questions__advanced","encrypted":"no","value":"no"},

{"name":"ssl_encryption_questions__help","encrypted":"no","value":"hide"}]}' | jq .

fi

if [ $delete == true ] ; then
       curl -sk -u admin:admin https://$bigip/mgmt/tm/sys/application/service/~Common~$appname.app~$appname -H 'Content-Type: application/json' -X DELETE | jq .
       echo "iAPP $appname deleted"   
fi 

Hello,

You may be interested in looking into Hitesh Patel's Application Services Integration iApp, which is designed to be a little simpler to deploy via the API. https://github.com/0xHiteshPatel/appsvcs_integration_iapp

The iApp builds in some sane defaults, which can ease the number of attributes you need to provide in your API calls. It also does not use self-populating fields, meaning, you need to provide all details you want to specify. This is a good thing, as typical iApps can require fairly complex API calls.

It's also compatible with systems like APIC, NSX, and Big-IQ.

-Josh