{"responseMessage":"Could not process template","responseCode":500}

I got the error message in the question title. The template works when I tested with Postman.
Here is the template:
<#if addHeader == true>
ExpensifyID, Timestamp, Merchant, Amount, Card, User, Description, GL Code, Job Code, Cost Code, Last Updated, Receipt<#lt>
</#if>
<#assign reportNumber = 1>
<#assign expenseNumber = 1>
<#list reports as report>
<#list report.transactionList as expense>
<#if expense.modifiedMerchant?has_content>
<#assign merchant = expense.modifiedMerchant>
<#else>
<#assign merchant = expense.merchant>
</#if>
<#if expense.convertedAmount?has_content>
<#assign amount = expense.convertedAmount/100>
<#elseif expense.modifiedAmount?has_content>
<#assign amount = expense.modifiedAmount/100>
<#else>
<#assign amount = expense.amount/100>
</#if>
<#if expense.modifiedCreated?has_content>
<#assign created = expense.modifiedCreated>
<#else>
<#assign created = expense.created>
</#if>
<#assign card = expense.cardNumber>
${expense.transactionID},<#t>
${created},<#t>
${merchant},<#t>
${amount},<#t>
${card},<#t>
${report.submitter.fullName},<#t>
${expense.comment},<#t>
${expense.ntag1GlCode},<#t>
${expense.ntag1GlCode},<#t>
${expense.ntag1GlCode},<#t>
${expense.inserted},<#t>
${expense.receiptFilename}<#lt>
<#assign expenseNumber = expenseNumber + 1>
</#list>
<#assign reportNumber = reportNumber + 1>
</#list>
Answers
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We solved the problem by URI encoding the template.