Parameter	Mandatory	Description	Examples	More Info
API	Yes	The API area	clients.json
General	Yes	Parameters described in overview	user=user&password=user	Structure of an API call
Model Structure	Yes	Name of model required	modelstructure=clientfinancial	Using data models
View	No	Stored filter applied		Using views
Sort	No	Change the view's default sort order	sort=CLIENT	Sorting
Filters	No	Filter by a key field		Filters
Company	Yes	The company number	company=1
Identifier	Yes	Client ID	client=1/P0909

Example request:

http://<SERVER>/jsonapi/clients.json?company=1&version=4&user=user&password=user&company=1&style=modeldata&modelstructure=clientfinancial&client=1/P0909

Example response:

{
  "responsecode": 1,
  "responsestatus": "OK",
  "errorcode": 0,
  "errormessage": "",
  "totalrows": 1,
  "totalpages": 1,
  "responsemessage": "",
  "pagerows": 0,
  "pagenumber": 1,
  "success": true,
  "data": [
    {
      "clientUuid": "CA1D229D72D8EB47A659669DD39FE48D",
      "clientTimeStampModified": 1554299566,
      "clientRecordVersionNumber": 16,
      "clientChargeTypeDescription": "Quote",
      "clientInvestment": 0,
      "clientTurnover": 0,
      "clientJobPhaseStatus": "Company Default",
      "clientTaxCodeDescripton": "1 (20%)",
      "clientCode": "26/C0127",
      "clientName": "Amazon",
      "clientMultiCurrency": true,
      "clientNominal": "",
      "clientNominalPurchase": "",
      "clientEbillingRef": "",
      "clientODCreditLimit": 0,
      "clientPaymentTermsDescription": "Immediate",
      "clientPaymentTermsInternal": 3,
      "clientPOMarkUp": true,
      "clientPOMarkUpPercent": 100,
      "clientPostingAccount": "",
      "clientChargeType": true,
      "clientCurrencycode": "",
      "clientCurrency": "- Base currency -",
      "clientInvestmentOpenBal": 0,
      "clientJobPrefix": "",
      "clientVatReg": "4344333",
      "clientTaxCode": 1,
      "clientTaxRate": 20,
      "clientDefaultStatus": 0
    }
  ]
}

Note: needs 12.2 for custom fields