after complete merchant validation when i passed response to completeMerchantValidation() method then "payment not completed" error occurred

Hi ,

I completed merchant validation from server side and pass its response to session.completeMerchantValidation() method .. but whenever i passed response to it "payment not completed " popup occurred , i used verified domain and certificates for apple pay web .

Code Block 
when i clicked on "buy now"	button it shows processing at end of the payment dialog (instead of showing button ) after completing merchant validation it gives payment not completed dialog	. so please help me for this.

front end code for session begin and merchant validation

const session_new = new ApplePaySession(10, ApplePayPaymentRequest);
session_new.begin();
//const session_new = new ApplePaySession(8, ApplePayPaymentRequest);

session_new.onvalidatemerchant = ({ validationURL }) => {
//alert("onvalidatemerchant11");
fetch('merchant validation url', {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify({validationURL: validationURL})
}).then(res => res.json())
.then(json => {
session_new.completeMerchantValidation(json);

}).catch((error) => {
alert(error+"------------- in line")
});

response from merchant validation url

{ epochTimestamp: 1619001540582,
expiresAt: 1619005140582,
merchantSessionIdentifier:
'SSHC6E3C328776A428687B2FEC0D1E02475_916523AAED1343F5BC5815E12BEE9250AFFDC1A17C46B0DE5A943F0F94927C24',
nonce: 'dca42609',
merchantIdentifier:'1736CEED7C7DF9B168D4D468C892DCEFFAD89C0D8FD5F03FC60F7131FE82B9BF',
domainName: 'my verified domain name',
signature:
'308006092a864886f70d010702a0803080020101310f300d06096086480165030402010500308006092a864886f7.......',
operationalAnalyticsIdentifier:
'apple signin:1736CEED7C7DF9B168D4........',
retries: 0 }

Code Block 
	 
					if something wrong with my code then also let me know