How to avoid Content-Length HTTP header is not numeric error on Azure app gateway

Question

We have an asp.net mvc application hosted in azure app service. The WAF policy on application gateway is blocking a post request with the "403 Forbidden" error. On firewall log, we see below error captured.

{
  "timeStamp": "2023-07-25T04:19:52+00:00",
  "resourceId": "XXXX",
  "operationName": "ApplicationGatewayFirewall",
  "category": "ApplicationGatewayFirewallLog",
  "properties": {
    "instanceId": "appgw_0",
    "clientIp": "XXXX",
    "requestUri": "/Account/ForgotPassword",
    "ruleSetType": "OWASP CRS",
    "ruleSetVersion": "3.2",
    "ruleId": "920160",
    "ruleGroup": "REQUEST-920-PROTOCOL-ENFORCEMENT",
    "message": "Content-Length HTTP header is not numeric.",
    "action": "Matched",
    "details": {
      "message": "Pattern match ^\\d+$ at REQUEST_HEADERS:content-length.",
      "data": "2",
      "file": "REQUEST-920-PROTOCOL-ENFORCEMENT.conf",
      "line": "130"
    },
    "hostname": "dev.abc.com",
    "transactionId": "3d76839b7988f5963773b6016e3098d5",
    "policyId": "133#_subscriptions_c0978b9d-b809-45f4-aa76-391ceb2cfdba_resourceGroups_XXX_1_providers_Microsoft.Network_ApplicationGatewayWebApplicationFirewallPolicies_WAF-azuswa1easasdfe318",
    "policyScope": "Global",
    "policyScopeName": "Global",
    "engine": "Azwaf"
  }
}

I inspected the post request in Network tab & I see a valid content-length header. So, I am unaware of why this traffic is blocked on gateway & what is workaround for this other than disabling the particular rule.