Hello Marcin,

Add Custom footer and for include custom layout and include layout in report template

<!------Footer---->
<template id="external_layout_footer_ept">
    <div class="footer">
        <div class="text-center" style="border-top: 1px solid black;">
            <ul t-if="not company.custom_footer" class="list-inline">
                <li t-if="company.phone">Phone: <span t-field="company.phone"/></li>

                <li t-if="company.fax and company.phone">&amp;bull;</li>
                <li t-if="company.fax">Fax: <span t-field="company.fax"/></li>

                <li t-if="company.email and company.fax or company.email and company.phone">&amp;bull;</li>
                <li t-if="company.email">Email: <span t-field="company.email"/></li>

                <li t-if="company.website and company.email or company.website and company.fax or company.website and company.phone">&amp;bull;</li>
                <li t-if="company.website">Website: <span t-field="company.website"/></li>
            </ul>

            <t t-if="company.custom_footer">
                <span t-raw="company.rml_footer"/>
            </t>

            <ul class="list-inline">
                <li>Page:</li>
                <li><span class="page"/></li>
                <li>/</li>
                <li><span class="topage"/></li>
            </ul>
        </div>
    </div>      
</template>

<!-- Layout -->
<template id="external_layout_ept">
	<t t-name="external_layout_ept">
	<t t-if="not o and doc">
		<t t-set="o" t-value="doc"/>
		</t>
	<t t-set="company" t-value="o.company_id"/>
	<t t-if="o and 'type' in o and o.type in ['out_invoice','out_refund']">
			<t t-if="o and o.sudo().company_id.parent_id">
				<t t-set="company" t-value="o.sudo().company_id.parent_id"/>
			</t>
	 	</t>
	 
   
   <t t-call="report.external_layout_header"/>

	<t t-raw="0"/>
	<t t-call="module_name.external_layout_footer_ept"/>    		 
	</t>
</template>


<!-----------Report(second line where layout is call)------------->
<t t-call="report.external_layout">  <!---Already There----->
<t t-call="module_name.external_layout_ept"> <!-----Replace with above one------->

Thanks,

<xpath expr="//ul[@name='financial_infos']">' cannot be located

This means Odoo is looking for the element you removed.  You need to put it back, and in your change make it invisible or override it.