btcpayserver/BTCPayServer/Views/UIPublic/PayButtonHandle.cshtml

@{
    Layout = "_LayoutSimple";
    var allErrors = ViewData.ModelState.Values.SelectMany(v => v.Errors.Select(b => b.ErrorMessage));
}

<div class="row">
    <div class="col-lg-12">
        <h2>Pay Button request failed</h2>
        @foreach (var error in allErrors)
        {
            <div class="alert alert-danger mt-4">@error</div>
        }
    </div>
</div>