message: fix(serializer): add backwards compatibility for bitcoin
diff: @@ -4,6 +4,7 @@ import { DeserializedSyncProtocol, SyncProtocolUtils } from 'airgap-coin-lib/dis
  import { parseIACUrl } from '../../utils/utils'
  import { StorageService, SettingsKey } from '../storage/storage.service'
  +import BigNumber from 'bignumber.js'
  @Injectable({
  providedIn: 'root'
  @@ -66,6 +67,12 @@ export class SerializerService {
  public async serialize(chunks: IACMessageDefinitionObject[]): Promise<string[]> {
  if (!this.useV2 && !chunks.some((chunk: IACMessageDefinitionObject) => chunk.protocol === 'cosmos')) {
  + if (chunks[0].protocol === 'btc' && chunks[0].type === 6) {
  + // This expects a BigNumber, but we now have a string. So we need to convert it.
  + const legacyPayload: any = chunks[0].payload
  + legacyPayload.amount = new BigNumber(legacyPayload.amount)
  + legacyPayload.fee = new BigNumber(legacyPayload.fee)
  + }
  return [await this.serializeV1(chunks[0])]
  } else {
  return this.serializeV2(chunks)
  