How do I access a particular key in square bracketed nested object like [{....}] using PHP strictly

Question

I use a GET method to call customers API end point, I get the response with all clients listed in JSON format. Am trying to access the "username" key in each of the clients. response is like below. just copied 2 clients for case reference. Have use the foreach loop but no data comes out. I need some help on the code to access key username which has to be an email value.

[
    {
        "id": 1,
        "userIdent": "YGSDJDF76D",
        "previousIsp": "Telkom ADSL 4mbps",
        "isLead": false,
        "clientType": 1,
        "companyName": null,
        "companyRegistrationNumber": null,
        "companyTaxId": null,
        "companyWebsite": null,
        "street1": "26 Place",
        "street2": "Merebank",
        "city": "Durban",
        "countryId": 263,
        "stateId": null,
        "zipCode": "4052",
        "fullAddress": "1 newark street",
        "invoiceStreet1": null,
        "invoiceStreet2": null,
        "invoiceCity": null,
        "invoiceStateId": null,
        "invoiceCountryId": null,
        "invoiceZipCode": null,
        "invoiceAddressSameAsContact": true,
        "note": null,
        "sendInvoiceByPost": null,
        "invoiceMaturityDays": null,
        "stopServiceDue": null,
        "stopServiceDueDays": null,
        "organizationId": 1,
        "tax1Id": null,
        "tax2Id": null,
        "tax3Id": null,
        "registrationDate": "2019-12-21T00:00:00+0200",
        "leadConvertedAt": null,
        "companyContactFirstName": null,
        "companyContactLastName": null,
        "isActive": true,
        "firstName": "Noor M C",
        "lastName": "Jooma",
        "username": "custmer3@gmail.com",
        
    },
    {
        "id": 2,
        "userIdent": 7892BC47G,
        "previousIsp": null,
        "isLead": false,
        "clientType": 1,
        "companyName": null,
        "companyRegistrationNumber": null,
        "companyTaxId": null,
        "companyWebsite": null,
        "street1": "59 Rd",
        "street2": "Mbank",
        "city": "urban",
        "countryId": 263,
        "stateId": null,
        "zipCode": "4052",
        "fullAddress": "new york, urban, 4052",
        "invoiceStreet1": null,
        "invoiceStreet2": null,
        "invoiceCity": null,
        "invoiceStateId": null,
        "invoiceCountryId": null,
        "invoiceZipCode": null,
        "invoiceAddressSameAsContact": true,
        "note": null,
        "sendInvoiceByPost": null,
        "invoiceMaturityDays": null,
        "stopServiceDue": null,
        "stopServiceDueDays": null,
        "organizationId": 1,
        "tax1Id": null,
        "tax2Id": null,
        "tax3Id": null,
        "registrationDate": "2019-12-21T00:00:00+0200",
        "leadConvertedAt": null,
        "companyContactFirstName": null,
        "companyContactLastName": null,
        "isActive": true,
        "firstName": "Ishtiyaak",
        "lastName": "Hatteea",
        "username": "i8596@gmail.com",
       
    }
]